Sound reducing wedge shaped polymer interlayers

ABSTRACT

The present invention is in the field of polymer interlayers and multiple layer glass panels comprising polymer interlayers, and, more specifically, the present invention is in the field of wedge shaped polymer interlayers.

FIELD OF THE INVENTION

The present invention is in the field of polymer interlayers andmultiple layer glass panels comprising polymer interlayers, and, morespecifically, the present invention is in the field of wedge shapedpolymer interlayers.

BACKGROUND

Poly(vinyl butyral) (PVB) is commonly used in the manufacture of polymersheets that can be used as interlayers in light-transmitting laminatessuch as safety glass or polymeric laminates. Safety glass often refersto a transparent laminate comprising a poly(vinyl butyral) sheet, orinterlayer, disposed between two sheets of glass. Safety glass often isused to provide a transparent barrier in architectural and automotiveopenings. Its main function is to absorb energy, such as that caused bya blow from an object, without allowing penetration through the openingor the dispersion of shards of glass, thus minimizing damage or injuryto the objects or persons within an enclosed area. Safety glass also canbe used to provide other beneficial effects, such as to reduceultraviolet (UV) and/or infrared (IR) light transmission, and/or enhancethe appearance and aesthetic appeal of window openings.

Safety glass interlayers have also been used as an important componentin automobile head-up display (HUD) systems, which can provide, forexample, an instrument cluster image at the eye level of a driver of theautomobile. Such a display allows a driver to stay focused on theupcoming road while visually accessing dash board information. One typeof interlayer used in such head-up display systems is wedge shaped invertical cross section. The wedge shape of the interlayer is used toprovide the correct light dynamics through the windshield required for ahead up display. Unfortunately, as with standard windshields, head updisplay windshields can also lead to an undesirablely high noisetransmission level through the windshield.

Accordingly, further improved compositions and methods are needed toenhance the sound dampening characteristics of multiple layer glasspanels, and specifically multiple layer glass panels in which a wedgeshaped interlayer is used to provide for head-up display capability.

SUMMARY OF THE INVENTION

The present invention provides interlayers that can be used in multiplelayer glass panel type applications to reduce the amount of soundtransmitted through the panel, and, in particular, at coincidentfrequencies for such glass laminates, for example in the range of about2,000 to 6,000 Hertz. This effect is achieved by incorporating anacoustic polymeric interlayer into wedge shaped laminated glassapplications, and, more specifically, into wedge shaped windshieldapplications.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of one embodiment of a wedge shapedinterlayer of the present invention.

DETAILED DESCRIPTION

Now, according to the present invention, it has been discovered thatwedge shaped windshield interlayers incorporating an acoustic polymersheet can advantageously be used to limit sound transmission through awindshield and into a vehicle. Wedge shaped interlayers of the presentinvention are particularly useful in automobiles in which a “heads up”display is provided and for which non-parallel glass layers aretypically used in the windshield laminate.

As will be described in detail herein, windshield interlayers of thepresent invention are wedge shaped. As used herein, an interlayer orpolymer sheet is said to be “wedge shaped” if the average thickness ofthe interlayer or polymer sheet as measured at one edge is at least 0.13millimeters greater than the average thickness of the interlayer orpolymer sheet as measured at the opposite edge. Wedge shaped interlayersof the present invention, in cross section, can resemble, for example,an isosceles trapezoid or a right trapezoid, among others, when they arefirst formed. The thickness transitions of the cross-section of thepolymer sheet can occur gradually, or can be immediate. The rate of thethickness change from one edge of the polymer sheet to the opposite edgecan be continuous, or can vary to the extent that the profile may beflat with no rate of thickness change in certain areas of the crosssection of the polymer sheet. Likewise, the rate of thickness change maydecrease or increase throughout the cross section of the polymer sheetas long as one edge of the polymer sheet is greater in thickness thanthe other edge. Of course, after lamination with non-planar rigidsubstrates such as curved glass windshields, the wedge shaped interlayerwill conform to the contours of the laminate.

The wedge shaped interlayers of the present invention can be formed froma single polymer sheet, or from two or more polymer sheets. As will bedescribed in detail below, polymer sheets can be any suitablethermoplastic polymer, for example poly(vinyl butyral).

In various embodiments, wedge shaped interlayers of the presentinvention are formed from a single polymer sheet. In variousembodiments, the polymer sheet can be a wedge shaped polymer sheet thathas been formed from a single acoustic polymer melt (as defined herein)in a single melt extrusion process. In other embodiments, a singlepolymer sheet can be formed through a coextrusion process in which anacoustic polymer melt and a non acoustic polymer melt (as definedherein) are coextruded to form a single wedge shaped polymer sheethaving an acoustic region and a non acoustic region. In variouscoextrusion embodiments, the regions are formed so as to approximate twoseparate layers within the single sheet, which emulates the effect thatwould be achieved if two separate polymer sheets—an acoustic and a nonacoustic—had been laminated together. In yet other embodiments, a firstacoustic polymer melt and a second, different acoustic polymer melt canbe coextruded to form a wedge shaped interlayer having two differentacoustic regions. Again, each region approximates a layer within thesheet.

For any of the coextrusion embodiments described in the previousparagraph, a further coextrusion region can be formed from acoustic ornon acoustic material, as desired. For example, a wedge shaped polymersheet can be formed by coextruding an acoustic polymer melt between twonon acoustic polymer melts to form a three region wedge shaped polymersheet that can be used as a noise suppressing interlayer. Thisembodiment has the advantage of relatively low blocking. Furthercoextrusion regions can be formed with tinted melts, for example, toform color gradient regions within the polymer sheet.

In any of the embodiments in which a single wedge shaped polymer sheetis used to form a wedge shaped windshield interlayer, one edge of thepolymer sheet can have an edge with a thickness that is at least 0.13millimeters, at least 0.2 millimeters, at least 0.3 millimeters, atleast 0.4 millimeters, at least 0.5 millimeters, at least 0.7millimeters, or at least 1.0 millimeters greater than the thickness ofthe opposite edge, which difference forms a wedge shape.

In any of the embodiments in which a single wedge shaped polymer sheetis used to form a wedge shaped windshield interlayer, the thinner edgecan have a thickness of, for example, at least 0.38 millimeters, atleast 0.45 millimeters, at least 0.75 millimeters, at least 1.0millimeters, and/or from 0.38 to 2.5 millimeters, 0.4 to 2.0millimeters, 0.5 to 1.75 millimeters, or 0.6 to 1.5 millimeters.

In various other embodiments, windshield interlayers of the presentinvention comprise more than one polymer sheet, and, optionally, otherpolymeric layers and/or other layers. In these embodiments, at least oneof the polymer sheets is an acoustic polymer sheet or a polymer sheethaving an acoustic region, as defined herein.

As shown in FIG. 1 generally at 10, a two layer embodiment comprises awedge shaped polymer sheet 14 and a flat polymer sheet 12. The wedgeshaped polymer sheet 14 and the flat polymer sheet 12 together form awedge shaped interlayer having a first thickness, T1, and a secondthickness, T2. As described above for single layer embodiments, one edgeof the wedge shaped interlayer can have an edge with a thickness (T2)that is at least 0.13 millimeters, at least 0.2 millimeters, at least0.3 millimeters, at least 0.4 millimeters, at least 0.5 millimeters, atleast 0.7 millimeters, or at least 1.0 millimeters greater than thethickness of the opposite edge (T1), which difference forms a wedgeshape. Further, T1, as shown in FIG. 1, can have a thickness of, forexample, at least 0.38 millimeters, at least 0.45 millimeters, at least0.75 millimeters, at least 1.0 mm, and/or from 0.38 to 2.5 millimeters,0.4 to 2.0 millimeters, 0.5 to 1.75 millimeters, or 0.6 to 1.5millimeters.

The schematic representation of one embodiment of a wedge shapedinterlayer of the present invention illustrated in FIG. 1 shows athickness transition of the cross-section of the polymer sheet thatoccurs immediately and at a continuous and constant rate of thethickness change.

For wedge shaped interlayer embodiments where the rate of thicknesschange from one edge of the polymer sheet to the opposite polymer sheetis continuous and constant, the wedge angle, formed between the wedgeshaped surface and the opposite surface, can be calculated from thealgorithm:

${\tan\;\alpha} = \frac{{T\; 2} - {T\; 1}}{W}$

Where α is the wedge angle, in milliradians; T1 and T2 are defined inFIG. 1, and W is the width of the wedge shaped interlayer sheet.

For wedge shaped interlayer embodiments of the present invention inwhich two or more layers are used, at least one of the layers is anacoustic polymer sheet or a coextruded polymer sheet having an acousticregion, as described above. For example, the wedge shaped polymer sheet14 can be an acoustic polymer sheet and the flat polymer sheet 12 can bea non acoustic polymer sheet. The reverse is also acceptable, where thewedge shaped polymer sheet 14 is a non acoustic polymer sheet and theflat polymer sheet 12 is an acoustic polymer sheet.

In yet further embodiments, one or more further layer of polymer sheetare incorporated into the construct shown in FIG. 1. For example, athird polymer sheet, acoustic or non acoustic and wedge shaped or nonwedge shaped can be incorporated. Any suitable configuration of polymersheets and sheet types can be used to form a wedge shaped interlayer,and in various embodiments, the overall dimensions of these multiplelayered interlayers will be within the ranges given above forthicknesses for single polymer sheet embodiments.

In various embodiments, a polymer film layer such as poly(ethyleneterephthalate), as described elsewhere herein, can be included in amultiple layer construct of the present invention. For example, apolymer film can be included between the wedge shaped polymer sheet 14and the flat polymer sheet 12 in FIG. 1 to produce a three layerembodiment in which a polymer film is incorporated between two polymerlayers. In yet further embodiments, two or more polymer films can beincorporated into multiple layer interlayer embodiments of the presentinvention.

In various embodiments of the present invention, interlayers of thepresent invention, when laminated between two sheets of glass panes,reduce the transmission of sound through the laminated glass panel by atleast 2 decibels (dB) at the coincident frequency relative to acomparable laminated glass panel having a single conventional interlayerconsisting of a non acoustic polymer sheet having the same shape as aninterlayer of the present invention.

In various embodiments of the present invention, interlayers of thepresent invention, when laminated between two sheets of glass panes,improve the sound transmission loss by at least 2 dB, more preferably 4dB, and even more preferably 6 dB or higher, say 8 dB at the coincidentfrequency relative to a comparable laminated glass panel having a singleconventional interlayer consisting of a non acoustic polymer sheethaving the same shape as an interlayer of the present invention.

For each embodiment described herein comprising a glass layer, anotherembodiment exists, where suitable, wherein a glazing type material isused in place of the glass. Examples of such glazing layers includerigid plastics having a high glass transition temperature (T_(g)), forexample above 60° C. or 70° C., for example polycarbonates, polyesters,polyalkyl methacrylates, and specifically those having from 1 to 3carbon atoms in the alkyl moiety.

In addition to the interlayers provided herein, the present inventionalso provides methods of reducing the level of sound through an opening,comprising the step of disposing in the opening a multiple layer glasspanel comprising any of the wedge shaped interlayers of the presentinvention.

The present invention also includes methods of manufacturing a multiplelayer glazing, comprising laminating any of the interlayers of thepresent invention between two rigid, transparent panels, as are known inthe art, such as glass or acrylic layers.

The present invention also includes multiple layer glass panels, such aswindshields and architectural windows, comprising a multiple layerinterlayer of the present invention. Also included are multiple layerglazing panels having plastics, such as acrylics, or other suitablematerials in place of the glass panels.

Polymer Film

As used herein, a “polymer film” means a relatively thin and rigidpolymer layer that functions as a performance enhancing layer. Polymerfilms differ from polymer sheets, as used herein, in that polymer filmsdo not themselves provide the necessary penetration resistance and glassretention properties to a multiple layer glazing structure, but ratherprovide performance improvements, such as infrared absorption orreflection character. Poly(ethylene terephthalate) is most commonly usedas a polymer film.

The polymer film is preferably optically transparent (i.e. objectsadjacent one side of the layer can be comfortably seen by the eye of aparticular observer looking through the layer from the other side), andusually has a greater, in some embodiments significantly greater,tensile modulus regardless of composition than that of an adjacentpolymer sheet. In various embodiments, the polymer film comprises athermoplastic material. Among thermoplastic materials having suitableproperties are nylons, polyurethanes, acrylics, polycarbonates,polyolefins such as polypropylene, cellulose acetates and triacetates,vinyl chloride polymers and copolymers and the like.

In various embodiments, the polymer film comprises materials such asre-stretched thermoplastic films having the noted properties, whichinclude polyesters. In various embodiments, the polymer film comprisesor consists of poly(ethylene terephthalate), and, in variousembodiments, the polyethylene terephthalate has been biaxially stretchedto improve strength, and/or has been heat stabilized to provide lowshrinkage characteristics when subjected to elevated temperatures (e.g.less than 2% shrinkage in both directions after 30 minutes at 150° C.).

An additional type of polymer film that can be used with the presentinvention, which is described in U.S. Pat. No. 6,797,396, comprises amultitude of nonmetallic layers that function to reflect infraredradiation without creating interference that can be caused by metalliclayers.

In various embodiments, the polymer film can have a thickness of 0.013millimeters to 0.20 millimeters, 0.025 millimeters to 0.10 millimeters,or 0.04 to 0.06 millimeters. The polymer film can optionally be surfacetreated or coated with a functional performance layer to improve one ormore properties, such as adhesion or infrared radiation reflection.These functional performance layers include, for example, a multi-layerstack for reflecting infra-red solar radiation and transmitting visiblelight when exposed to sunlight. This multi-layer stack is known in theart (see, for example, WO 88/01230 and U.S. Pat. No. 4,799,745) and cancomprise, for example, one or more Angstroms-thick metal layers and oneor more (for example two) sequentially deposited, optically cooperatingdielectric layers. As is also known (see, for example, U.S. Pat. Nos.4,017,661 and 4,786,783), the metal layer(s) may optionally beelectrically resistance heated for defrosting or defogging of anyassociated glass layers. Various coating and surface treatmenttechniques for poly(ethylene terephthalate) film and other polymer filmsthat can be used with the present invention are disclosed in publishedEuropean Application No. 0157030. Polymer films of the present inventioncan also include a hardcoat and/or and antifog layer, as are known inthe art.

Polymer Sheet

As used herein, a “polymer sheet” means any thermoplastic polymercomposition formed by any suitable method into a thin layer that issuitable alone, or in stacks of more than one layer, for use as aninterlayer that provides adequate penetration resistance and glassretention properties to laminated glazing panels. Plasticized poly(vinylbutyral) is most commonly used to form polymer sheets.

Polymer sheets of the present invention are acoustic polymer sheets ornon acoustic polymer sheets. As used herein, an “acoustic polymer sheet”is a polymer sheet that has a glass transition temperature of less than25° C. and that causes an improved sound transmission loss, as definedelsewhere herein and which can be measured as described elsewhereherein, of at least 2 decibels. In various embodiments, acoustic polymersheets of the present invention have glass transition temperatures ofless than 25° C., less than 20° C., less than 15° C., or less than 10°C., while being greater than −15° C. Non acoustic polymer sheets arepolymer sheets that both do not have a glass transition temperatures ofless than 25° C. and that cause an improvement in sound transmissionloss of less than 2 decibels when compared with an otherwise equivalentpolymer sheet having a glass transition temperature of between 30-33° C.Further, as used herein, an “acoustic polymer melt” is any polymer meltthat, when formed into a polymer sheet, has the qualities just describedfor an acoustic polymer sheet, and a “non acoustic polymer melt” is anypolymer melt that, when formed into a polymer sheet, has the qualitiesjust described for a non acoustic polymer sheet.

A single polymer melt that is used to form a wedge shaped polymer sheetcan be formed through the blend of two or more different polymericmaterials. In some embodiments, a single polymer sheet can exhibitmultiple glass transition temperatures. A polymer sheet formed throughsuch a melt that has at least one glass transition temperature less than25° C., as used herein, is said to have a glass transition temperatureof less than 25° C.

A single polymer sheet that is formed through a coextrusion process inwhich an acoustic polymer melt and a non acoustic polymer melt arecoextruded to form a single wedge shaped polymer sheet having anacoustic region and a non acoustic region can have two or more glasstransition temperatures in which at least one of the glass transitiontemperatures is less than 25° C. and at least one of the glasstransition temperatures is greater than 25° C.

Similarly, a wedge shaped interlayer that comprises an acoustic polymersheet and a non acoustic polymer sheet, wherein at least one of thepolymer sheets is wedge shaped, can have multiple glass transitiontemperatures wherein at least one of the glass transition temperaturesis less than 25° C. and at least one of the glass transition temperatureis greater than 25° C.

The polymer sheet can comprise any suitable polymer, and, in a preferredembodiment, the polymer sheet comprises poly(vinyl butyral). In any ofthe embodiments of the present invention given herein that comprisepoly(vinyl butyral) as the polymeric component of the polymer sheet,another embodiment is included in which the polymer component consistsof or consists essentially of poly(vinyl butyral). In these embodiments,any of the variations in additives disclosed herein can be used with thepolymer sheet having a polymer consisting of or consisting essentiallyof poly(vinyl butyral).

In one embodiment, the polymer sheet comprises a polymer based onpartially acetalized poly(vinyl alcohol)s. In another embodiment, thepolymer sheet comprises a polymer selected from the group consisting ofpoly(vinyl butyral), polyurethane, polyvinyl chloride, poly(ethylenevinyl acetate), combinations thereof, and the like. In otherembodiments, the polymer sheet comprises plasticized poly(vinylbutyral). In further embodiments the polymer sheet comprises poly(vinylbutyral) and one or more other polymers. Other polymers having asuitable glass transition temperature can also be used.

In any of the sections herein in which preferred ranges, values, and/ormethods are given specifically for poly(vinyl butyral) (for example, andwithout limitation, for plasticizers, component percentages,thicknesses, and characteristic-enhancing additives), those ranges alsoapply, where applicable, to the other polymers and polymer blendsdisclosed herein as useful as components in polymer sheets.

For embodiments comprising poly(vinyl butyral), the poly(vinyl butyral)can be produced by known acetalization processes that involve reactingpoly(vinyl alcohol) with butyraldehyde in the presence of an acidcatalyst, followed by neutralization of the catalyst, separation,stabilization, and drying of the resin, with the understanding that invarious embodiments, residual hydroxyl content will be controlled, asdescribed elsewhere herein.

In various embodiments, the polymer resin can comprise less than 25 wt.% residual ester groups, 20 wt. %, 15 wt. %, 10 wt. %, 7 wt. %, 5 wt. %,or less than 3 wt. % residual ester groups calculated as polyvinylacetate, with the balance, other than residual hydroxyl, being anacetal, preferably butyraldehyde acetal, but optionally including otheracetal groups in a minor amount, e.g., a 2-ethyl hexanal group (see, forexample, U.S. Pat. No. 5,137,954).

In various embodiments it is advantageous to use poly(vinyl butyral)having a residual poly(vinyl alcohol) content, by weight, of 9% to 50%,10% to 50%, 11% to 40%, 15% to 30%, or 20% to 30%, although other rangescan be used as well. It is also advantageous in some applications to usepoly(vinyl butyral) having a residual poly(vinyl alcohol) content, byweight, of greater than 25%, greater than 27%, or greater than 30%.

In various embodiments, the polymer sheet comprises poly(vinyl butyral)having a molecular weight greater than 30,000, 40,000, 50,000, 55,000,60,000, 65,000, 70,000, 120,000, 250,000, or 350,000 grams per mole(g/mole or Daltons). Small quantities of a dialdehyde or trialdehyde canalso be added during the acetalization step to increase molecular weightto greater than 350 Daltons (see, for example, U.S. Pat. Nos. 4,874,814;4,814,529; and 4,654,179). As used herein, the term “molecular weight”means the weight average molecular weight.

In various embodiments of polymer sheets of the present invention, nonacoustic polymer sheets can comprise 10 to 90, 15 to 85, 20 to 60, 25 to60, 20 to 80, 25 to 70, and 25 to 60 parts plasticizer per hundred resin(“phr”) parts. Of course other quantities can be used as is appropriatefor the particular application. The poly(vinyl butyral) sheet preferablycomprises 20 to 80, and more preferably 25 to 60, parts plasticizer perone hundred parts of resin. In some embodiments, the plasticizer has ahydrocarbon segment of less than 20, less than 15, less than 12, or lessthan 10 carbon atoms. The amount of plasticizer can be adjusted toaffect the glass transition temperature of the poly(vinyl butyral)sheet.

Conventional, non acoustic poly(vinyl butyral) interlayer typically hasa glass transition temperature in the range of 30-33° C. Acousticpoly(vinyl butyral) can differ from non acoustic interlayer in variousways, including modification to the mole ratio of the average amount ofethylene groups bonded to acetyl groups, the degree of acetalization,the length of aldehyde groups, and/or the amount of plasticizer. Forinstance, the acoustic interlayer can be obtained by increasing theconcentration of plasticizer and/or with a reduction in the hydroxylcontent of the polyvinyl butyral resin, sufficient to reduce the glasstransition temperature from about 30° C. to about 18° C. or lower. Ingeneral, higher amounts of plasticizer are added to decrease the glasstransition temperature. In various embodiments of the present invention,an acoustic polymer sheet comprises, for example, 30-100 phr ofplasticizer, 40-90 phr of plasticizer, 50-85 phr of plasticizer, or60-80 phr of plasticizer.

Acoustic polymer sheets can also be obtained by using an unmodifiedpoly(vinyl butyral) that is typically used in conventional interlayer, acompatiblizer agent, and a plasticizer. The role of the compatiblizeragent is to make the poly(vinyl butyral) resin and the plasticizer morecompatible to reduce the glass transition temperature of the interlayer.The compatiblizer can be added at 2 to 50 phr. Examples of compatiblizeragents include, but are not limited to, tri-ethylene glycol,tetra-ethylene glycol or oligomers of ethylene glycols; propylene glycoland its oligomers; tri-ethylene glycol mono-(2-ethylhexanoate), andother alkyl, aryl hydrocarbons containing ethylene glycol or propyleneglycol moieties, and their chemical derivatives.

Any suitable plasticizers can be added to the polymer resins of thepresent invention in order to form the polymer sheets. Plasticizers usedin the polymer sheets of the present invention can include esters of apolybasic acid or a polyhydric alcohol, among others. Suitableplasticizers include, for example, triethylene glycoldi-(2-ethylbutyrate), triethylene glycol di-(2-ethylhexanoate),triethylene glycol diheptanoate, tetraethylene glycol diheptanoate,dihexyl adipate, dioctyl adipate, hexyl cyclohexyladipate, mixtures ofheptyl and nonyl adipates, diisononyl adipate, heptylnonyl adipate,dibutyl sebacate, polymeric plasticizers such as the oil-modifiedsebacic alkyds, and mixtures of phosphates and adipates such asdisclosed in U.S. Pat. No. 3,841,890 and adipates such as disclosed inU.S. Pat. No. 4,144,217, and mixtures and combinations of the foregoing.Other plasticizers that can be used are mixed adipates made from C₄ toC₉ alkyl alcohols and cyclo C₄ to C₁₀ alcohols, as disclosed in U.S.Pat. No. 5,013,779, and C₆ to C₈ adipate esters, such as hexyl adipate.In preferred embodiments, the plasticizer is triethylene glycoldi-(2-ethylhexanoate).

Adhesion control agents (ACAs) can also be included in the polymersheets of the present invention to impart the desired adhesiveness.These agents can be incorporated into the outer sheets in a threepolymer sheet embodiment, for example. Any of the ACAs disclosed in U.S.Pat. No. 5,728,472 can be used. Additionally, residual sodium acetateand/or potassium acetate can be adjusted by varying the amount of theassociated hydroxide used in acid neutralization. In variousembodiments, polymer sheets of the present invention comprise, inaddition to sodium acetate, magnesium bis(2-ethyl butyrate)(chemicalabstracts number 79992-76-0). The magnesium salt can be included in anamount effective to control adhesion of the polymer sheet to glass.

Additives may be incorporated into the polymer sheet to enhance itsperformance in a final product. Such additives include, but are notlimited to, plasticizers, dyes, pigments, stabilizers (e.g., ultravioletstabilizers), antioxidants, flame retardants, other IR absorbers,anti-block agents, combinations of the foregoing additives, and thelike, as are known in the art.

Agents that selectively absorb light in the visible or near infraredspectrum can be added to any of the appropriate polymer sheets. Agentsthat can be used include dyes and pigments such as lanthanum hexaboride(LaB₆), indium tin oxide, and antimony tin oxide.

As used herein, “resin” refers to the polymeric (for example poly(vinylbutyral)) component that is removed from the mixture that results fromthe acid catalysis and subsequent neutralization of the polymericprecursors. Resin will generally have other components in addition tothe polymer, for example poly(vinyl butyral), such as acetates, salts,and alcohols. As used herein, “melt” refers to a mixture of resin with aplasticizer and, optionally, other additives.

Any suitable method can be used to produce the polymer sheets and themultiple layer interlayers of the present invention. Details of suitableprocesses for making poly(vinyl butyral) are known to those skilled inthe art (see, for example, U.S. Pat. Nos. 2,282,057 and 2,282,026). Inone embodiment, the solvent method described in Vinyl Acetal Polymers,in Encyclopedia of Polymer Science & Technology, 3^(rd) edition, Volume8, pages 381-399, by B. E. Wade (2003) can be used. In anotherembodiment, the aqueous method described therein can be used. Poly(vinylbutyral) is commercially available in various forms from, for example,Solutia Inc., St. Louis, Mo. as Butvar™ resin.

One exemplary method of forming a poly(vinyl butyral) layer comprisesextruding molten poly(vinyl butyral) comprising resin, plasticizer, andadditives and then forcing the melt through a sheet die (for example, adie having an opening that is substantially greater in one dimensionthan in a perpendicular dimension). A sheet die can be used to producethe wedge shaped polymer sheet in such a way that the die opening iscontrolled and/or altered across the width of the die to produce thedesired wedge thickness profile while melt is being forced through thedie. Wedge shaped layers can be formed by using an appropriately wedgeshaped sheet die.

Another exemplary method of forming a poly(vinyl butyral) layercomprises casting a melt from a die onto a roller, solidifying theresin, and subsequently removing the solidified resin as a sheet. Ineither embodiment, the surface texture at either or both sides of thelayer may be controlled by adjusting the surfaces of the die opening orby providing texture at the roller surface. Other techniques forcontrolling the layer texture include varying parameters of thematerials (for example, the water content of the resin and/or theplasticizer, the melt temperature, molecular weight distribution of thepoly(vinyl butyral), or combinations of the foregoing parameters).Furthermore, the layer can be configured to include spaced projectionsthat define a temporary surface irregularity to facilitate the de-airingof the layer during lamination processes after which the elevatedtemperatures and pressures of the laminating process cause theprojections to melt into the layer, thereby resulting in a smoothfinish.

Polymer sheets of the present invention that comprise acoustic and nonacoustic regions can be produced by any method known in the art. In atypical method, two or more melts comprising polymer resin, plasticizer,and any desired additives can be independently formed and coextruded toform a single polymer sheet having regions corresponding to each meltused. For example a first melt that, if used alone, would result in asheet with a glass transition temperature of 20° C., and a second meltthat, if used alone, would result in a sheet with a glass transitiontemperature of 30° C., can be coextruded to form a polymer sheet havinga first region and a second region, each approximating the shape of anindividual sheet, wherein the first region has a glass transitiontemperature of 20° C. and the second region has a glass transitiontemperature of 30° C.

Interlayers of the present invention that comprise more than one polymersheet can be produced through a calendaring or pre-lamination process.In a typical method, an acoustic polymer sheet and a non acousticpolymer sheet, wherein at least one of the sheets is wedge shaped, arecombined under pressure and heat to form an interlayer. The acousticpolymer sheet, if wedge shaped, is formed through a single polymer meltor through a coextrusion process as described in various embodiments inthe previous paragraphs.

The following paragraphs describe various techniques that can be used toimprove and/or measure the characteristics of the polymer sheet.

The clarity of a polymer sheet, and particularly a poly(vinyl butyral)layer, can be determined by measuring the haze value, which is aquantification of the amount of light scattered away from the directionof the incident beam in passing through the layer. The percent haze canbe measured according to the following technique. An apparatus formeasuring the amount of haze, a Hazemeter, Model D25, which is availablefrom Hunter Associates (Reston, Va.), can be used in accordance withASTM D1003-61 (Re-approved 1977)-Procedure A, using Illuminant C, at anobserver angle of 2 degrees. In various embodiments of the presentinvention, percent haze is less than 5%, less than 3%, and less than 1%.

The visible transmittance can be quantified using a UV-Vis-NIRspectrophotometer such as the Lambda 900 made by Perkin ElmerCorporation by methods described in international standard ISO9050:1990. In various embodiments, the transmittance through a polymersheet of the present invention is at least 60%, at least 70%, or atleast 80%.

Pummel adhesion can be measured according to the following technique,and where “pummel” is referred to herein to quantify adhesion of apolymer sheet to glass, the following technique is used to determinepummel. Two-ply glass laminate samples are prepared with standardautoclave lamination conditions. The laminates are cooled to about −18°C. (0° F.) and manually pummeled with a hammer to break the glass. Allbroken glass that is not adhered to the poly(vinyl butyral) layer isthen removed, and the amount of glass left adhered to the poly(vinylbutyral) layer is visually compared with a set of standards. Thestandards correspond to a scale in which varying degrees of glass remainadhered to the poly(vinyl butyral) layer. In particular, at a pummelstandard of zero, no glass is left adhered to the poly(vinyl butyral)layer. At a pummel standard of 10, 100% of the glass remains adhered tothe poly(vinyl butyral) layer. Poly(vinyl butyral) layers of the presentinvention can have, for example, a pummel value of between 3 and 10.

The “yellowness index” of a polymer sheet can be measured according tothe following: Transparent molded disks of polymer sheet 1 cm thick,having smooth polymeric surfaces which are essentially plane andparallel, are formed. The index is measured according to ASTM method D1925, “Standard Test Method for Yellowness Index of Plastics” fromspectrophotometric light transmittance in the visible spectrum. Valuesare corrected to 1 cm thickness using measured specimen thickness. Invarious embodiments of the present invention, a polymer sheet can have ayellowness index of 12 or less, 10 or less, or 8 or less.

As used herein glass transition temperature of polymer sheets isdetermined by rheometric dynamic shear mode analysis using the followingprocedure. A thermoplastic polymer sheet is molded into a sample disc of25 millimeters (mm) in diameter. The polymeric sample disc is placedbetween two 25 mm diameter parallel plate test fixtures of a RheometricsDynamic Spectrometer II (available from Rheometrics, Incorporated,Piscataway, N.J.). The polymer sheet sample disc is tested in shear modeat an oscillation frequency of 1 Hertz as the temperature of the sampleis increased from −20° C. to 70° C. at a rate of 2° C./minute. Theposition of the maximum value of tan delta (damping) plotted asdependent on temperature is used to determine glass transitiontemperature.

As used herein, conventional laminated glass is formed throughlaminating a conventional interlayer consisting of a non-acousticpolymer sheet having the same shape as an interlayer of the presentinvention between two sheets of rigid glass panes. For the purpose ofthe present invention, the conventional laminated glass is referred toas “reference laminate panel”.

Improvement in acoustic insulation as used to characterize glasslaminates consisting of the interlayers of the present invention isdetermined with reference to a reference laminate panel as described inprevious paragraph. In typical laminates with two outer layers of glass,the “combined glass thickness” is the sum of the thickness of the twolayers of glass; in more complex laminates with three or more layers ofglass, the combined glass thickness would be the sum of the three ormore layers of glass.

For purposes of the present invention a “coincident frequency” means thefrequency at which a panel exhibit a dip in sound transmission loss dueto “coincident effect” (see Lu, J; Windshields with New PVB Interlayerfor Vehicle Interior Noise Reduction and Sound Quality Improvement—SAEPaper # 2003-01-1587). The coincident frequency of the reference panelis typically in the range of 2,000 to 6,000 Hertz, and can beempirically determined from a monolithic sheet of glass having athickness equal to the combined glass thickness of glass in thereference panel from the algorithm

$\begin{matrix}{f_{c} = \frac{15\text{,}000}{d}} & \;\end{matrix}$where “d” is the total glass thickness in millimeters and “f_(c)” is inHertz.

For purposes of this invention, improvement in acoustic performance canbe measured by an increase in sound transmission loss at the coincidentfrequency (reference frequency) of the reference panel.

“Sound transmission loss” is determined for a laminate of the presentinvention or conventional reference panel of fixed dimensions with ASTME90 (95) at a fixed temperature of 20° C.

Glass laminates using interlayers of the present invention can beprepared by known procedures, for example as disclosed in U.S. Pat. Nos.5,024,895; 5,091,258; 5,145,744; 5,189,551;5,264,058 and 5,529,654.Preferred glass is heat strengthened, float glass and may be tinted orcoated with metal and/or metal oxide layers to reflect specific portionsof the electromagnetic spectrum, for example, infrared. Preferred glasslaminates are made with glass that is not more than 3.2 mm thick,preferably thinner, for example not more than 2.5 mm thick, and morepreferably not more than 2.3 mm thick. A glass laminate can compriseglass of different thicknesses, for example 1.6 mm and 2.3 mm. In atypical safety glass lamination process, a three layer assembly ofglass, polymer interlayer, and glass is assembled and heated to a glasstemperature of about 25° C. to 50° C. and then passed through a pair ofnip rolls to expel trapped air. The compressed assembly is then heated,for example by infrared radiation or in a convection oven, to atemperature of about 60° C. to 110° C. for a short period, for exampleabout 1 to 5 minutes. The heated assembly is then passed through asecond pair of nip rolls followed by autoclaving the assembly at about130° C. to 150° C. and about 1,000 to 2,000 kilo Pascals for about 30minutes. Non-autoclave methods as disclosed in U.S. Pat. No. 5,536,347are also useful.

EXAMPLES

The following examples are intended to illustrate and not limit orrestrict the scope of the invention. Laminates used to illustrate theinvention are prepared using the following materials:

3GEH: triethylene glycol di(2-ethylhexanoate) plasticizer.

Glass: annealed float glass in thickness of 2.1 or 2.3 millimeters.

PVB: Non wedge shaped poly(vinyl butyral) having 18.7% hydroxyl content,containing 38 phr 3GEH and having a glass transition temperature of 30°C., at a thickness of 0.38 mm (15 mil).

C-PVB: Conventional wedge shaped poly(vinyl butyral) having 18.7%hydroxyl content, containing 38 phr 3GEH and having a glass transitiontemperature of 30° C., at a thickness in one edge of the sheet of 0.76mm (30 mil) and on the opposite edge of 1.14 mm (45 mil), and a sheetwidth of 1,000 mm.

A-PVB1: Non-wedge shaped acoustic poly(vinyl butyral) having low (16%)hydroxyl content, containing 50 phr 3GEH plasticizer, having a glasstransition temperature of 18° C., and being 0.5 mm (20 mil) thick.

A-PVB2: Wedge shaped acoustic poly(vinyl butyral) having low (16%)hydroxyl content, containing 50 phr 3GEH plasticizer, having a glasstransition temperature of 18° C., at a thickness in one edge of thesheet of 1.0 mm and on the opposite edge of 1.42.

A-PVB3: Non-wedge shaped co-extruded three-layer acoustic poly(vinylbutyral) being 0.80 mm thick, wherein two outer layers containing 38 phr3GEH and having a glass transition temperature of about 30° C. and theinner layer having low (12%) hydroxyl content, containing 75 phr 3GEHplasticizer, having a glass transition temperature of about 2° C., andbeing 0.13 mm (5 mil) thick.

Panels for acoustic testing comprising glass with various polymericinterlayers are constructed into 48×75 cm panels of components assembledas indicated in Tables 1 through 4. PVB interlayer film is conditionedin a humidity cabinet to a targeted moisture level of 0.43%, and handlaid up on a glass sheet preheated to 40° C. In case of panelscontaining multilayer interlayer the individual layers are stacked onthe preheated glass in the order indicated. A second glass sheetpreheated to 40° C. is placed on top of the stacked interlayer sheets.The panel is then compressed by passing through nip rollers adjusted to40 psig to de-air the structure and to tack the interlayer to the glasssurface. The “de-aired” panel is placed in a preheated oven at 105° C.for about 20 minutes and passed through the nip rollers a second timefor further de-airing and to edge seal the panel. The panel is then airautoclaved (heated at elevated temperature and pressure).

TABLE 1 (Prior Art) No. Interlayer Components Wedge Angle, mrad T_(g) (°C.) 1 PVB 0 30 2 C-PVB 0.38 30

TABLE 2 (Prior Art, Reference Panels) Coincident STL at coincident No.Interlayer Glass* Freq. (Hz) freq (dB) 3. C-PVB 2.1-mm 4000 31 4. C-PVB2.3-mm 3150 31 *Glass laminate consists of glass sheet/interlayer/glasssheet. The thickness of each glass sheet is indicated in the Tableabove.

TABLE 3 No. Interlayer Components Wedge Angle, mrad T_(g) (° C.) 5A-PVB2 0.42 18 6 A-PVB2/PVB 0.42 18 and 30 7 A-PVB1/C-PVB 0.38 18 and 308 A-PVB3/C-PVB 0.38  2 and 30 9 A-PVB1/A-PVB2 0.42 18

TABLE 4 STL at the Improvement No. Interlayer components* reference freq(dB) in STL (dB) 10 A-PVB2 38 7 11 A-PVB2/PVB 38 7 12 A-PVB1/C-PVB 37 613 A-PVB3/C-PVB 38 7 *Glass laminates for STL measurements consist ofglass sheet/interlayer components/glass sheet. The thickness of eachglass sheet is 2.1-mm.

By virtue of the present invention, it is now possible to provideacoustic wedge shaped interlayers that reduce sound transmission througha windshield.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiments disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present inventioncan be used interchangeably with any ranges, values, or characteristicsgiven for any of the other components of the invention, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout. For example, a polymer sheet canbe formed comprising wedge shapes in any of the ranges given in additionto any of the ranges given for plasticizer, where appropriate, to formmany permutations that are within the scope of the present invention butthat would be cumbersome to list.

Any figure reference numbers given within the abstract or any claims arefor illustrative purposes only and should not be construed to limit theclaimed invention to any one particular embodiment shown in any figure.

Figures are not drawn to scale unless otherwise indicated.

Each reference, including journal articles, patents, applications, andbooks, referred to herein is hereby incorporated by reference in itsentirety.

1. A windshield interlayer, comprising: a plasticized poly(vinylbutyral) polymer sheet comprising 40-90 phr plasticizer and having aglass transition temperature of less than 25° C., wherein saidwindshield interlayer is wedge shaped and has a first edge and a secondedge, wherein said first edge has a thickness of at least 0.38millimeters and said second edge has a thickness that is at least 0.13millimeters greater than said thickness of said first edge, and whereinsaid polymer sheet shows an improved sound transmission loss of at leasttwo decibels relative to an equivalent polymer sheet having a glasstransition temperature between 30-33 ° C.
 2. The windshield interlayerof claim 1, wherein said windshield interlayer further comprises asecond polymer sheet.
 3. The windshield interlayer of claim 2, whereinsaid second polymer sheet is not wedge shaped and said polymer sheethaving a glass transition temperature of less than 25° C. is wedgeshaped.
 4. The windshield interlayer of claim 2, wherein said secondpolymer sheet is wedge shaped and said polymer sheet having a glasstransition temperature of less than 25° C. is not wedge shaped.
 5. Thewindshield interlayer of claim 2, further comprising a polymer filmlayer disposed between said polymer sheet having a glass transitiontemperature of less than 25° C. and said second polymer sheet.
 6. Thewindshield interlayer of claim 1, wherein said thickness of said secondedge is 0.13 millimeters to 0.8 millimeters greater than said thicknessof said first edge.
 7. The windshield interlayer of claim 6, whereinsaid thickness of said second edge is 0.3 millimeters to 0.8 millimetersgreater than said thickness of said first edge.
 8. The windshieldinterlayer of claim 6, wherein said first thickness is at least 0.5millimeters.
 9. The windshield interlayer of claim 1, wherein said wedgeshaped polymer interlayer does not comprise polymer sheets other thansaid polymer sheet having a glass transition temperature of less than25° C.
 10. The windshield interlayer of claim 9, wherein said polymersheet having a glass transition temperature of less than 25° C.comprises an acoustic region and a non acoustic region.
 11. Thewindshield interlayer of claim 1, wherein said windshield interlayerfurther comprises a polymer film.
 12. The windshield interlayer of claim1 wherein said plasticized poly(vinyl butyral) polymer sheet has aresidual hydroxyl content of less than 18.7%.
 13. The windshieldinterlayer of claim 12 wherein said plasticized poly(vinyl butyral)polymer sheet has a residual hydroxyl content of less or equal to than16%.
 14. The windshield interlayer of claim 1 wherein said plasticizeris triethylene glycol di-(2-ethylhexanoate).
 15. A method formanufacturing a windshield interlayer comprising: forming a wedge shapedwindshield interlayer comprising a plasticized poly(vinyl butyral)polymer sheet comprising 40 -90 phr plasticizer and having a glasstransition temperature of less than 25° C. wherein said windshieldinterlayer has a first edge and a second edge, wherein said first edgehas a thickness of at least 0.38 millimeters and said second edge has athickness that is at least 0.13 millimeters greater than said thicknessof said first edge, and wherein said polymer sheet shows an improvedsound transmission loss of at least two decibels relative to anequivalent polymer sheet having a glass transition temperature between30 -33° C.
 16. The method of claim 15, further comprising forming asecond polymer sheet and laminating said second polymer sheet and saidpolymer sheet having a glass transition temperature of less than 25° C.17. The method of claim 16, wherein said second polymer sheet is notwedge shaped and said polymer sheet having a glass transitiontemperature of less than 25° C. is wedge shaped.
 18. The method of claim16, wherein said second polymer sheet is wedge shaped and said polymersheet having a glass transition temperature of less than 25° C. is notwedge shaped.
 19. The method of claim 16, further comprising a polymerfilm layer disposed between said polymer sheet having a glass transitiontemperature of less than 25° C. and said second polymer sheet.
 20. Themethod of claim 15, wherein said thickness of said second edge is 0.13millimeters to 0.8 millimeters greater than said thickness of said firstedge.
 21. The method of claim 20, wherein said thickness of said secondedge is 0.3 millimeters to 0.8 millimeters greater than said thicknessof said first edge.
 22. The method of claim 21, wherein said thicknessof said first edge is at least 0.5 millimeters.
 23. The method of claim15, wherein said wedge shaped polymer interlayer does not comprisepolymer sheets other than said polymer sheet having a glass transitiontemperature of less than 25° C.
 24. The method of claim 15, furthercomprising laminating a polymer film to said polymer sheet having aglass transition temperature of less than 25° C.
 25. The method of claim16, further comprising forming said polymer sheet having a glasstransition temperature of less than 25° C. by coextruding an acousticpolymer melt and a non acoustic polymer melt to form said polymer sheethaving a glass transition temperature of less than 25° C., wherein saidpolymer sheet is wedge shaped and comprises an acoustic region and a nonacoustic region.
 26. The method of manufacturing a windshield interlayerof claim 15 wherein said plasticized poly(vinyl butyral) polymer sheethas a residual hydroxyl content of less than 18.7%.
 27. The method ofmanufacturing a windshield interlayer of claim 26 wherein saidplasticized poly(vinyl butyral) polymer sheet has a residual hydroxylcontent of less or equal to than 16%.
 28. The method of manufacturing awindshield interlayer of claim 15 wherein said plasticizer istriethylene glycol di-(2-ethylhexanoate).
 29. A windshield comprising: awindshield interlayer, comprising: a plasticized poly(vinyl butyral)polymer sheet comprising 40-90 phr plasticizer and having a glasstransition temperature of less than 25° C., wherein said windshieldinterlayer is wedge shaped and has a first edge and a second edge,wherein said first edge has a thickness of at least 0.38 millimeters andsaid second edge has a thickness that is at least 0.13 millimetersgreater than said thickness of said first edge, and wherein said polymersheet shows an improved sound transmission loss of at least two decibelsrelative to an equivalent polymer sheet having a glass transitiontemperature between 30-33° C.
 30. The windshield of claim 29, whereinsaid windshield interlayer further comprises a second polymer sheet. 31.The windshield of claim 30, wherein said second polymer sheet is notwedge shaped and said polymer sheet having a glass transitiontemperature of less than 25° C. is wedge shaped.
 32. The windshield ofclaim 30, wherein said second polymer sheet is wedge shaped and saidpolymer sheet having a glass transition temperature of less than 25° C.is not wedge shaped.
 33. The windshield of claim 30, further comprisinga polymer film layer disposed between said polymer sheet having a glasstransition temperature of less than 25° C. and said second polymersheet.
 34. The windshield of claim 29, wherein said thickness of saidsecond edge is 0.13 millimeters to 0.8 millimeters greater than saidthickness of said first edge.
 35. The windshield of claim 34, whereinsaid thickness of said second edge is 0.3 millimeters to 0.8 millimetersgreater than said thickness of said first edge.
 36. The windshield ofclaim 34, wherein said first thickness is at least 0.5 millimeters. 37.The windshield of claim 29, wherein said wedge shaped polymer interlayerdoes not comprise polymer sheets other than said polymer sheet having aglass transition temperature of less than 25° C.
 38. The windshield ofclaim 37, wherein said polymer sheet having a glass transitiontemperature of less than 25° C. comprises an acoustic region and a nonacoustic region.
 39. The windshield of claim 29, wherein said windshieldinterlayer further comprises a polymer film.
 40. The windshield of claim29 wherein said plasticized poly(vinyl butyral) polymer sheet has aresidual hydroxyl content of less than 18.7%.
 41. The windshield ofclaim 40 wherein said plasticized poly(vinyl butyral) polymer sheet hasa residual hydroxyl content of less or equal to than 16%.
 42. Thewindshield of claim 29 wherein said plasticizer is triethylene glycoldi-(2-ethylhexanoate).
 43. A windshield interlayer, comprising: acoextruded multilayer plasticized poly(vinyl butyral) polymer sheetcomprising 40-90 phr plasticizer and having a region with a glasstransition temperature of less than 25° C. and a region with a glasstransition temperature of greater than 25° C., wherein said windshieldinterlayer is wedge shaped and has a first edge and a second edge andwherein said first edge has a thickness of at least 0.38 millimeters andsaid second edge has a thickness that is at least 0.13 millimetersgreater than said thickness of said first edge, and wherein said polymersheet shows an improved sound transmission loss of at least two decibelsrelative to an equivalent polymer sheet having a glass transitiontemperature between 30-33° C.
 44. The windshield interlayer of claim 43wherein said plasticized poly vinyl butyral) polymer sheet has aresidual hydroxyl content of less than 18.7%.
 45. The windshieldinterlayer of claim 44 wherein said plasticized poly(vinyl butyral)polymer sheet has a residual hydroxyl content of less or equal to than16%.
 46. The windshield interlayer of claim 44 wherein said plasticizeris triethylene glycol di-(2-ethylhexanoate).